What software can I use to flip my moniter's screen along horizontally
(a-axis) to create a mirrored image?

I have an Nvidia Geforce graphics card and am aware of the rotate
functions that come with the drivers but there does not appear to be a
mirror function. I need this as I am building a projector from an old
moniter. The software needs to be usable under windows.

Also if nothing can be found I would accept software that merely flips
standard PC video formats ie dvd, divx and vcd.